Housing
What size is your tank? 2.5
What temperature is your tank? 82
Does your tank have a filter? no
Does your tank have an air stone or other type of aeration? no
Is your tank heated? yes
What tank mates does your betta fish live with? none

Food
What type of food do you feed your betta fish? Hikari Betta Bio-Gold
How often do you feed your betta fish? 4 to 5 pellets a day
Maintenance
How often do you perform a water change? 50% mid week 100% end of week
What percentage of the water do you change when you perform a water change? same as above.
What type of additives do you add to the water when you perform a water change? Prime

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia:
Nitrite:
Nitrate:
pH:
Hardness:
Alkalinity:

Symptoms and Treatment
How has your betta fish's appearance changed? Bloated
How has your betta fish's behavior changed? No
When did you start noticing the symptoms? 3 days ago
Have you started treating your fish? If so, how? Yes.. Epsom salt
Does your fish have any history of being ill? No
How old is your fish (approximately)?

Hikari tends to lend itself to this problem because of its high wheat content. I would look for another pellet.. one whose first two or three ingredients are whole fish, not fish meal or wheat.

You're also feeding on the high end.. that's not to say that some bettas are okay with that but you could easily cut that back to 3-4 and he'd be fine. Maybe he'd be less prone to constipation. Also whatever you feed you should do one fast day a week, as that will also help keep him regular.

The epsoms should get him moving. When he does poop I expect it to be a round ball the color of his pellets. If it's white, clear or mucas like then he has an infection too.

Personally I like and feed New Life Spectrum Betta. They're smaller so you can feed more. My smallest get 5 a day and my biggest get 8. I split them into two feedings and fast one day a week. Omega One Betta Buffet is another one. It's more the size of your Hikari you're used to.

IAL won't help with constipation but it can help with stress and infection.

I find epsoms more effective than daphnia but it wouldn't hurt to have it on hand. Some enjoy it and you could feed a little pellet sized chunk once a week to keep them regular. It's an option, but not necessary.